Clearing abrasion marks from photographic emulsions



Aug-18, 1936. P. p. BREWSTER CLEARING ABRASION MARKS FROM PHOTOGRAPHIQ EMULSIONS d'riginal Filed June 1, 1953 2 Sheets-Sheet 1 ATTORNEY Aug. 18, 19.36. p D, BREWSTER 2,051,798

CLEARING ABRASION MARKS FROM PHOTOGRAPHIC EMULSIONS Original Filed June 1, 1933 2 Sheets-Sheet 2 @INEER E ATTORNEY Patented Aug. 18, 1936 PATENT OFFICE CLEARING ABRASION MARKS FROM PHOTOGRAPHIC EMULSIONS Percy Douglas Brewster, Eatontown, N. J.

Refiled for (abandoned) application Serial No.

673,800, June 1, 14, 1936, Serial No. September 29, 1934 '7 Claims.

My invention relates to the clearing of developable marks or abrasions in photographic silver halide emulsions before development, specially on motion picture film.

The object of my invention is to destroy or reduce to a minimum all latent markings in either negative or positive emulsions due to scratches, rubbing, abrasion or pressure marks before development without appreciably afiecting the speed of the emulsion or any latent image due to exposure to light ifthe emulsion layer 'on the film was cleared after being exposed.

It is well known that any slight scratch or rub on a photographic emulsion will appear, after development, as a black mark of varying density,

, due to the silver being reduced at that point by the developer. Motion picture film is specially liable to abrasions while being coated and perforated, and from passing through motion picture 20 cameras, sound recording cameras or printers.

Abrasion marksso slight as to be of little importance on black and white motion picture film are converted, by certain processes used in making color motion pictures, into fiashes of brilliant color that are very objectionable.

I am aware that means have been suggested for treating photographic emulsions to remove latent abrasion marks and emulsion fog but, I believe, that all of these proposed methods used liquid reagents that affected the silver grains in the emulsion and also tended to reduce the speed of the emulsion. By the means described in this invention, the silver grains, that have not been rendered devolopable or latent by the abrasions, are not affected in any way by the clearing agent as far as I can see or determine by the instruments available to me. The speed of the emulsion (if cleared before exposure) or the latent photographic image (if cleared after exposure) 40 are not afiected except that in the exact spot where a heavy mark has been made, the photographic image may be slightly lighter.

Throughout the specification and claims it is to be understood that latent abrasion mar refers to any abrasion, rub, scratch or pressure mark in the emulsion that can be developed; and that 'clearing or destroying latent abrasion marks means that these marks are either actu- 50 ally destroyed or converted into substances which In accordance with this invention, there is provided an improved method of clearing latent abrasion marks from silver halide photographic emulsions before development, which comprises are not developedby ordinary developing means.-

1933. This application May 79,757. In Great Britain passing the emulsion through an atmosphere containing an oxidizing gas or vapor.

I have found that not all oxidizing gases or vapours are of equal usefulness in clearing abrasion marks from silver halide emulsions. Some 5 oxidizing gases are so weak in their action on the emulsion that they do not quite sufilciently clear the abrasions, although they undoubtedly have some effect in clearing the abrasions, while other oxidizing gases or vapors are sufliciently strong to 10 min the emulsion and even to affect the celluloid base. Where an oxidizing gas or vapor of the latter type is used, its concentration will, of course, have to be adjustedto give the amount of clearing action desired without injuriousl'y afiecting 1 the emulsion.

The film is treated in preferably dry state with the gas, and the oxidizing gas destroys all but the most latent abrasion marks without appreciably afiecting the speed of the emulsion or the latent 20 photographic image.

As indicated above, have this clearing effect in varying degrees. way of example, cessfully used:-

oxidizing gases and vapors By Halogens (bromine, chlorine and iodine) Oxides of nitrogen, such as nitric oxide and nitrogen tetroxide, (N204) Bromine or other clearing agent that exists normally in liquid form may be diluted with any liquid, miscible with it, that has a suitable vapor pressure provided it does not have a bad effect on the emulsion or celluloid base. Gaseous clearing agents if desired may be diluted with fixed amounts of air or other inert gas.

If iodine is used it should preferably be slightly heated, as, for example, by circulating warm air over iodine crystals. However, any other suitable method of producing iodine vapor may be used.

While I prefer to clear the abrasion marks from the emulsion immediately before development, the emulsion layer on the film may be treated with gas as soonas coated, after being perforated (if motion picture film), or before exposure without departing from my invention. If motion picture film is to be developed by machine, I preferto apply'the gas to the film in a tube or receptacle which is a part of the developing machine so the 50 film is not handled after clearing but is immediately developed.

A gas, such as properly diluted bromine, allowed to act on the emulsion layer on the film at normal temperature and humidity (approximately 68 deg. 55

the following gases may be suc- F. and 50% humidity) long enough to clear but all the most severe abrasion marks and the emulsion layer on the film then thoroughly washed if the film has been exposed, no appreciable effect on the latent photographic image. If the content of moisture in the film or the humidity in the gas treating chamber be too high, or if the film is not immediately developed, the clearing gas remaining in the emulsion may result in loss of photographic detail or the speed of the emulsion may be reduced. This effect seems to be increased if the cleared emulsion is stored some time before being developed. Thorough washing with air reduces this tendency. It is possible that some of the clearing gas may be dissolved in the moisture within the emulsion and continue the clearing action for some time causing a loss of the photographic efiect.

- I believe that these clearing gases, particularly if they are reasonably dry, due to their physical structure, do not penetrate as deeply into the emulsion as liquids would, but are confined more or less to the surface where the abrasion marks lie. By not penetrating so deeply there is less tendency for gases to alter the photographic characteristics of the emulsions.

It is not necessary in order'to remove all ordinary abrasion marks to clear the emulsionon the film with pure bromine gas, which is very powerful and has a tendency to attack the celluloid base, so I prefer to dilute it below its normal vapor pressure with a predetermined amount of air or other inert gas to the point that it will destroy all but the most severe of the latent abrasion marks in about a minute without affecting the celluloid base.

In the preferred method one part of liquid bromine is mixed with from five to twenty parts of carbon tetrachloride and the emulsion on the film treated for about a minute in a receptacle containing the vapors from these liquids at room temperature and medium humidity (about 68 deg. F. and 50% humidity). If the abrasion marks are slight the strength of the gas or time of application can be reduced. The moisture in the emulsion or humidity in the clearing gas may be materially increased without affecting seriously the speed of the emulsion or any latent'photographic image in the emulsion, specially if the emulsion be developed quickly after clearing. Bromine or other clearing agents that comesin liquid form may be diluted with any liquid, miscible with it, that has a suitable vapor pressure provided it does not have a bad efiect on the emulsion or celluloid base. Gaseous clearing agents if desired may be diluted with fixed amounts of air or other inert gas.

The exact concentration of bromine, or any other clearing gas or the time of treatment is of little consequence as long as it removes all but the most severe abrasion marks and does not damage the emulsion or base. In practice positive double coated motion picture film is fed at thirty feet per minute through a tube containing vapor from a ten to one mixture of carbon tetrachloride and bromine at 68 deg. F. and humidity of 60%, the film being in contact with the clearing gas for about thirty seconds. After treatment the film is "washed for several minutes with air as dry as possible before rewinding, to prevent any possibility of the continuing action of the clearing agent on the emulsion, and in the case of poisonous gases, to enable the film to be safely handled in the dark room. I

Any gas can be used that will completely or partly clear the emulsion of abrasion marks before development without departing from my invention. The film may be cleared in any type of apparatus desired. Several types that proved satisfactory in operation are illustrated in the accompanying drawings.

Figure 1 is a side elevation, partly in section, of the film treating apparatus;

Figure 2 is a similar view of a modified apparatus; and

Figure 3 is a similar view of a combined clearing and developing machine.

The film I is drawn from the feed-off reel 2 by the sprocket 3, to form the necessary loop. The film, drawn by sprocket 4 (operated in unison with sprocket 3 by a suitable mechanism driven by motor 5), passes under take-up weight 6, over guide I into the gas treating tube 8, under a bottom roller 9 and over a top roller guide into washing tubes H and I2, guided by similar rollers. After passing the sprocket 4, the film is wound upon a reel l3.

Bromine or other liquids either pure or diluted with other substances to reduce their vapor pressure, are placed in receptacles l4 and Ma and air is passed over the liquid to take up the vapor, which is drawn into the-inlet of a fan l5, driven by a motor I 6, and delivered into the bottom of the treating tube 8. The top of the treating tube is connected through the receptacle Ma to the receptacle I 4 by a tube I'I, so that by the action of the fan, a constant stream of air passes through the liquid receptacle to pick up vapor from the treating liquid and carries it through the treating tube. Gas can be fed from cylinders directly into A suitable cover I8 is mounted over the top-of the treating and air washing tubes. A fan l9, driven by a motor 20, exhausts the air from the cover I8 and draws air into the washing tubes II and I2 through inlets 20, 20, as well as serving to 'draw off any gas escaping from the treating tube 8, and exhausting this gas, which may be poisonous, to the atmosphere.

A chamber 2| is provided immediately in front of the chamber 8 and serves the purpose of preventing poisonous gases from escaping into the atmosphere owing to its being in connection with the chamber I 8 in which a partial vacuum is maintained by means of the exhauster l9.

The apparatus shown in Figure 2 is exactly similar to that shown in Figure 1 except that the liquid clearing agent is placed in a receptacle 22 and stirred by an agitating paddle 23, driven by a motor 24. Sufficient mixing of vapor with the air in the tube is usually secured by this method, in fact, the passage of the film through the treating tube causes air currents that are sometimes sufiicient to mix the vapor and the air without any other method of agitation.

In Figure 3 a portion of a combined clearing and developing machine is shown. The film I, either positive or negative, is guided by rollers 25, 26 through the gas labyrinth 21, where any escaping gas is drawn off through tube 28 by an exhauster. The film is then guided by a roller 29 into a gas treating chamber 30, under a fixed roller 3| to a guide roller 32. This chamber is shown divided by partition 33 so that the move: ment of the film will help circulate the gas to maintain an even concentration throughout. The 

